Clinical outcomes of type III Pseudomonas aeruginosa bacteremia*

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Background:Pseudomonas aeruginosa bacteremia is a serious and life-threatening infection associated with high mortality. Among the multitude of virulence determinants possessed by P. aeruginosa, the type 3 secretion system has been implicated with more acute and invasive infection in respiratory diseases. However, the relationship between the type 3 secretion system and clinical outcomes in P. aeruginosa bacteremia has not been investigated.Objectives:To determine the association between the type 3 secretion system virulence factor in P. aeruginosa bloodstream infection and 30-day mortality.Design:Retrospective analysis of 85 cases of P. aeruginosa bacteremia.Setting:Tertiary care hospital.Interventions:Bacterial isolates were assayed in vitro for secretion of type 3 exotoxins (ExoU, ExoT, and ExoS). Strain relatedness was analyzed using randomly amplified polymorphic DNA polymerase chain reaction genotyping. Antimicrobial susceptibilities were determined by means of the Kirby-Bauer disk-diffusion test.Measurements and Main Results:At least one of the type 3 secretion system proteins was detected in 37 out of the 85 isolates (44%). Septic shock was identified in 43% of bacteremic patients with type 3 secretion system+ isolates compared to 23% of patients with type 3 secretion system– isolates (p = .12). A high frequency of resistance in the type 3 secretion system+ isolates was observed to ciprofloxacin (59%), cefepime (35%), and gentamicin (38%). There was a significant difference in the 30-day cumulative probability of death after bacteremia between secretors and nonsecretors (p = .02). None of the type 3 secretion system+ patients who survived the first 30 days had a P. aeruginosa isolate which exhibited ExoU phenotype.Conclusions:The expression of type 3 secretion system exotoxins in bacteremic isolates of P. aeruginosa confers poor clinical outcomes independent of antibiotic susceptibility profile. (Crit Care Med 2012; 40:–1163)

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